Dispensing modules are commonly used to dispense viscous liquids, such as hot melt adhesives, in a variety of dispensing applications employed in the manufacture of products and in product packaging. Conventional dispensing modules are provided with either electrically actuated or electro-pneumatically valve assemblies that regulate the flow and discharge of liquid from the module. Typically, the valve assembly incorporates a needle that is movable within the body of the dispensing module for selectively displacing a tip of the needle relative to a valve seat between open and closed positions. In the closed position, the tip seals against the valve seat with a continuous line of contact that discontinues liquid flow to a dispensing orifice. Cyclic movement between the open and closed positions intermittently interrupts flow to generate a pattern of liquid on a receiving surface of the product or product packaging.
In certain dispensing modules, the dispensing orifice is provided in a nozzle which is itself removably attached to the body of the dispensing module. The ability to remove the nozzle from the body of the dispensing module has certain benefits. For example, the nozzle may be detached from the body for removing foreign debris, such as particles originating from charred viscous liquid, blocking the dispensing orifice or the liquid passageway leading to the dispensing orifice.
Under certain circumstances, it may be desirable to change the diameter of the dispensing orifice in order to modify an attribute of the liquid dispensing operation. For example, the diameter change may either increase or decrease the amount of liquid being dispensed. As another example, the diameter change may alter the abruptness of the liquid cut-off when the needle tip is moved from the open position to contact the valve seat to provide the closed position. Moreover, the dispensing orifice diameter may require changing if the orifice repeatedly clogs because of the type of liquid being dispensed, a change in the type of liquid being dispensed, or a change in the characteristics of the dispensing operation.
In certain conventional dispensing modules, the valve seat of the nozzle and the needle tip constitute a matched pair manufactured with corresponding dimensional tolerances. Any attempt to exchange one nozzle of one dispensing orifice diameter for another nozzle of a different dispensing orifice diameter in such dispensing modules often results in leakage due to an inability to provide an adequate sealing engagement between the needle tip and valve seat of the new nozzle. One source of leakage is misalignment between the needle tip and valve seat of the new nozzle such that the line of contact between the two is not continuous. Another source of leakage arises due to wear and erosion of the needle tip and valve seat, which creates correlated surface features in each after a sufficient number of cycles. Placing the nozzle carrying a used valve seat on a different dispensing module having a needle tip with non-correlated surface features creates leakage paths for the liquid past their line of contact when the needle tip is contacting the valve seat. In such dispensing modules, therefore, the diameter of the dispensing orifice may be changed only by replacing the existing dispensing module with a dispensing module having a different orifice diameter.
What is needed, therefore, is a nozzle for a liquid dispensing module that is freely interchangeable among various different dispensing modules independent of the cycle life of either the nozzle or the needle of the dispensing module.